Question

A rubber ball weighs 49 N.. a) What is the mass of the ball? (Answer: 5.0 kg). b) What is the acceleration of the ball if an upward force of 69 N is applied? (Answer: 4.0 m/s/s). For a) I used the equation W = Fg = mg, which becomes 49 = m(9.8). This approximates m to 5.0 kg.
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For b) I used the equation
ΣFy=Fa−W=ma
which becomes 69-49 = 20 N.
I then use equation F = ma which becomes 20 = 5.0a, which makes a
4.0m/s2

Answer 1

The answer you presented is correct.

For a) I used the equation W = Fg = mg, which becomes 49 = m(9.8). This approximates m to 5.0 kg.
For b) I used the equation
ΣFy=Fa−W=ma which becomes 69-49 = 20 N.
I then use equation F = ma which becomes 20 = 5.0a, which makes a 4.0m/s2